In most known CT scanners, which typically include/an array of x-ray detectors, electrical noise can significantly degrade performance of the detectors, and therefore degrade the overall performance of the CT scanner. Consequently, much effort is spent finding the sources of such electrical noise, and developing ways to eliminate the effects of electrical noise within the CT scanner.
For example, in a CT scanner having an array of semiconductor x-ray detectors, the typical detector comprises a crystal for converting x-ray photons into visible light photons, and a photodiode for converting the visible light photons into extremely low-amplitude (on the order of picoamperes to nanoamperes) electrical currents representative of the x-ray flux incident on the detector. The extremely low-amplitude currents are transmitted via an array of respective conductors to a data acquisition system (DAS) for signal processing.
However, the extremely low-amplitude currents are vulnerable to interference when they are exposed to sources of low-level ambient electrical noise. Such noise can be caused by minute motions of the detector, called microphonics, which induce noise via the triboelectric effect. Noise can also be caused by small ambient voltage fluctuations that produce undesirable electrical interference often referred to as pickup.
Each detector and the DAS must be grounded. It is known to use the return lines of the detectors to connect the detectors to the system ground, as shown in FIG. 2 and described in greater detail hereinafter. However, large currents flowing in the system ground can produce noise, with voltage fluctuations on the order of millivolts not being unusual. Thus, grounding a detector to the system ground via a return line can expose the detector to undesirable electrical noise. In addition, voltage fluctuations on the mounting structure of the detectors can also subject the detector to undesirable pickup.
Moreover, there are signal sources outside the detectors that can capacitively couple to the photodiodes of the detectors to produce currents going back to the input of the DAS via the return lines of the detectors, thereby creating a (usually AC) potential differential across the return lines of the detectors and DAS ground. Although the potential difference is small, e.g., typically on the order of millivolts, it can adversely affect the performance of a sensitive instrument, such as a CT scanner.